What Does a High Sodium Blood Test Mean?

A high sodium blood test usually means there is too little water in the body relative to the amount of sodium, rather than too much salt in the diet. The medical name is hypernatraemia (hypernatremia in US spelling). The most common cause is drinking less water than the body needs or losing extra fluid, for example through diarrhoea, heavy sweating or water tablets.

Sodium is a mineral that helps control fluid balance, nerves and muscles. The American Academy of Family Physicians defines hypernatraemia as a sodium level above 145 mEq per litre (the same as mmol/L). Laboratories set their own reference ranges, so compare your result with the range printed on your report. MedlinePlus notes that a result outside the range does not always mean a medical condition.

If your result is low rather than high, the separate guide to a low sodium blood test covers that pattern.

High sodium can affect the brain, and very high levels can be life-threatening without treatment. Call emergency services or go to an emergency department if someone has a high sodium result or signs of dehydration together with any of the following.

• New confusion, agitation or behaviour that is unusual for them.
• Being much sleepier than normal or hard to wake.
• A seizure, muscle twitching or collapse.
• Fast or difficult breathing, or cold, pale, grey, blue or blotchy skin, lips or tongue. The NHS warns these can be signs of shock.
• Passing very little or no urine alongside any of the signs above.

According to the American Academy of Family Physicians, hypernatraemia most commonly results from not taking in enough water. That can happen because thirst is reduced, water is hard to reach, or the body loses more water than usual. Gaining extra salt is a much less common cause.

MedlinePlus and the AAFP list causes that include:

• Dehydration from not drinking enough.
• Fluid loss from diarrhoea or heavy sweating.
• Diuretics (water tablets) and other causes of passing large amounts of urine.
• Kidney disease or a disorder of the adrenal glands.
• Diabetes insipidus, which is uncommon.
• Taking in too much salt, which is rare.

The NHS lists older adults, babies and young children as the groups most at risk of dehydration. The AAFP notes that people at the extremes of age are more likely to develop high sodium because they may depend on others to give them drinks. Poor mobility and memory or thinking problems add to the risk.

In practice, an older person may not feel thirsty, or may forget to drink. If you care for someone, keep drinks within easy reach, offer them regularly, and tell their care team about reduced eating or drinking, a new infection, diarrhoea or a change in alertness. Do not change the amount of fluid someone has been told to drink, or stop a prescribed medicine, without speaking to their clinician.

Mild high sodium may cause no obvious symptoms, or only general ones. MedlinePlus lists thirst, passing very little urine, vomiting, diarrhoea, confusion, muscle twitching and seizures. The AAFP notes that symptoms in adults are often vague, such as tiredness, sluggishness and weakness.

Signs of dehydration often appear alongside. The NHS lists thirst, a dry mouth, headache, dizziness, dark yellow and strong-smelling urine, passing urine less often, tiredness and sunken eyes. Because older people may not report thirst, confusion or drowsiness may be the first change others notice.

Diabetes insipidus is a rare condition, unrelated to type 1 or type 2 diabetes, in which the body passes large volumes of dilute urine and the person feels very thirsty. The NHS explains it involves a problem with the hormone arginine vasopressin, which helps the body hold on to water. NIDDK describes several types, including central and nephrogenic forms.

People with diabetes insipidus can become dehydrated quickly if they cannot drink enough to replace what they lose. The AAFP notes that dilute urine in someone who is dehydrated suggests the condition, and a water deprivation test can confirm it. The NHS advises seeing a GP if you feel thirsty all the time or are passing much more urine than usual.

Treatment focuses on finding and treating the cause and replacing the missing water. The AAFP describes using water by mouth or feeding tube when possible, and fluids through a drip when needed. Clinicians lower sodium gradually and check blood levels during treatment, because correcting it too fast can cause harm; in babies, overly fast correction has been linked to seizures.

Do not try to correct a high sodium result at home by drinking very large amounts of water quickly or by using salt substitutes or supplements. Follow the plan from the clinician who has your results.

Bring the report showing the sodium value, its unit, the reference range and the sample date, along with any earlier results and a list of medicines, including water tablets.

• How high is my sodium compared with the laboratory range, and has it changed from earlier tests?
• What do you think is the main cause: not drinking enough, fluid loss, a medicine or something else?
• Do my other results, such as kidney tests and urine tests, suggest diabetes insipidus or another condition?
• How much should I or the person I care for drink each day, and does a medical condition limit fluids?
• Should any medicine be reviewed, and who will decide that?
• When will the test be repeated, and which symptoms mean I should seek urgent help first?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a high sodium result, dehydration in an older relative or suspected diabetes insipidus described their situation can help you notice useful details, such as fluid intake, medicines and recent illness, and turn them into clear questions.

Similar cases cannot explain your own result, and we do not diagnose or recommend treatment. Use them to prepare for the conversation with your own care team.